Transition resonance for bridge-type converters has been described in U.S. Pat. Nos. 4,864,479 and 4,912,622 of R. L. Steigerwald and K.D.T. Ngo, assigned to the present assignee and incorporated by reference herein. Such circuits typically use four power switches (FET's) for high power applications, e.g., 200 Watts and greater. Although there is only one power processing magnetic component, i.e., transformer or inductor, it is impractical to use these circuits with four switches and associated gate drivers for lower power (less than 50 Watts) applications due to the relatively high costs associated therewith. Quasi-resonant and multi-resonant circuits are usually used for lower power conversion at high frequencies with a single power FET. However, although such resonant circuits have only one power FET, they typically have several resonant components (resonant inductors and capacitors) that cause inefficiencies and higher voltage or current stresses on the FET.
Accordingly, it is desirable to provide a dc-to-dc power converter that is amenable to high-density packaging techniques and very high frequency operation (e.g., 1-10MHz). It is further desirable to require only a single main power switch, rather than multiple power switching devices. Still further, it is desirable to achieve zero-voltage switching (i.e., switching with zero-voltage across a switching device) without the need for additional resonant circuit components.